Which of the following compound is added to the sodium extract before addition of silver nitrate for testing of halogens?

Question

Canvas Classes · Accepted Answer

Step 1: Understand the Purpose of the Pre-Treatment

In Lassaigne's test, after sodium fusion, the extract may contain:
-  (if N present)
-  (if S present)
-  (if halogen present, X = Cl, Br, I)

To test for halogens,  is added. The problem is that  and  ions would give interfering precipitates:
-  — looks identical to 
-  — masks any halide precipitate

Step 2: Why Acidify with Nitric Acid?

Adding dilute  (and boiling) decomposes  and :

Both  and  escape as gases. Only  remains, and:

Step

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